INFLUENCE OF SIZE AND DENSITY OF BROWSE PATCHES ON INTAKE RATES AND FORAGING DECISIONS OF YOUNG MOOSE AND WHITE-TAILED DEER

We examined the functional response and foraging behavior of young moo se (Alces alces) and white-tailed deer (Odocoileus virginianus) relati ve to animal size and the size and distribution of browse patches. The animals were offered one, three, or nine stems of dormant red maple ( Acer rubrum) in hand-assembled patches spaced 2.33, 7, 14, or 21 m apa rt along a runway. Moose took larger twig diameters and bites and had greater dry matter and digestible energy intake rates than did deer, b ut had lower cropping rates. Moose and deer travelled at similar veloc ities between patches and took similar numbers of bites per stem. We f ound that a model of intake rate, based on the mechanics of cropping, chewing, and encountering bites, effectively described the intake rate of moose and deer feeding in heterogeneous distributions of browses. As patch size and density declined, the animals walked faster between patches, cropped larger bites, and cropped more bites per stem, and he nce, dry matter intake rates remained relatively constant. As is chara cteristic of many hardwood browse stems, however, potential digestible energy concentration of the red maple stems declined as the size and number of bites removed (i.e., stem diameter at point of clipping) by the animals increased. Therefore, the digestible energy content of the diet declined with decreasing patch size and density. Time spent fora ging within a patch increased as patch size increased and as distance between patches increased, which qualitatively supported the marginal- value theorem. However, actual patch residence times for deer and moos e exceeded those predicted by the marginal-value theorem (MVT) by appr oximately 250%. The difference between actual and predicted residence time may have been a result of(I) an unknown or complex gain function, (2) the artificial conditions of the experiments, or (3) assumptions of MVT that do not apply to herbivores.